I'm too lazy to check, but I seem to remember a system for writing virtual file-systems in Perl for Linux. I don't know if that involved embedding Perl in the kernel, but it seems like it might have!
I wrote RFC: Fuse::DBI - mount database as filesystem about such virtual file-system (which mounts part of database). It uses Fuse perl bindings, so it embeds fuse into kernel and then just calls it from perl. It's very powerfull, but in strange file-system way.
I think you mean PerlFS, of course it is entirely crack induced - but it does actually work and I have heard of some people actually finding a use for it.